BOSTON — Almost five months into a rocky grind of a regular season, the Houston Rockets resemble the contender-caliber team that James Harden expected them to be.

“It feels really, really good to kind of have a full roster and catch a rhythm,” Harden said after the Rockets’ 115-104 victory over the Boston Celtics on Sunday, which extended the NBA’s longest active win streak to five games. “This is a perfect time for it.

“We haven’t had an opportunity to push, push, push. This is a perfect time to push, push, push and catch a groove going into the postseason.”

Will the Lakers make the playoffs? Kevin Pelton breaks down the tightest races.

The Rockets have had a longer win streak this season, when they reeled off six wins in a row in late December and early January immediately after Chris Paul suffered a strained hamstring that sidelined him for more than a month. But Houston knew that success wasn’t sustainable and that a healthy, productive Paul was needed for the Rockets to make a deep playoff run.

Paul continued his best stretch of the season with a 15-point, six-rebound, 12-assist, three-steal performance in Sunday’s win over the Celtics. The Rockets’ streak started when Paul had 23 points and 17 assists to lead them to a road win over the Golden State Warriors, despite Harden sitting out due to a cervical strain.

Center Clint Capela is still working his way into peak form after missing 15 games before the All-Star break due to ligament damage in his right thumb that required surgery, and key midseason pickups Kenneth Faried (hip) and Iman Shumpert (calf) didn’t play Sunday due to nagging injuries. However, Harden thinks the Rockets’ pieces are fitting better than they have at any point this season.

“We’re catching a rhythm,” said Harden, who scored 42 points in the win over the Celtics. “Throughout the course of the year, we’ve been having a lot of injuries, a lot of ups and downs, but we’re finally catching a rhythm on both ends of the floor, and it feels great.

The Rockets, who were 14th in the Western Conference standings after stumbling to an 11-14 start, are 38-25 and one game out of the No. 3 seed. Houston is 19-9 when Harden, Paul and Capela all play, including 5-1 since the All-Star break.

“Everybody knew we weren’t going to finish 14th,” said forward PJ Tucker, the Rockets’ defensive stopper who had a critical steal to seal the win over the Celtics. “That was out. We just had to find ourselves — new team, new roster, a lot of different things. We said all year, even when we were 14th, that we’re just going to keep chipping away at it, keep trying to play our best basketball until April and then get ready to roll.

“We don’t care what place we fall in. We just want to be playing our best basketball when the playoffs come.”